Papers by Keyword: Al-Mg

Abstract: In this study, commercial Al-3%Mg aluminium alloy was subjected to ECAP processing using two different ECAP die configurations. The first one – conventional and the second one modified in which a part of the exit channel in the ECAP die, causes twist deformation, to impose extra shear strains to the sample. The local changes in microstructure were characterized by Light Microscopy, SEM equipped with an EBSD facility and TEM. Mechanical properties of the ECAP processed samples were compared based on hardness measurement. The results showed that when ECAP with modified die, the greater grain and crystalline refinement is possible. The microstructures exhibit high dislocation density within subgrains with non-equilibrium and Moiré boundaries. Moreover, the mechanical examinations display a significant improvement in hardness and calculated yield strength when the ECAP process is conducted using a modified die.

Abstract: The wetting behavior of SiC by molten Al and Al-Mg alloys using the sessile-drop testing equipment was investigated. The results showed that Mg has a remarkable influence on the wettability and reaction in the Al/SiC system. The contact angle between SiC substrate and molten Al-Mg alloys decreased more quickly with increasing of Mg content. The transition temperature from non-wetting to wetting dropped with increasing of Mg content, suggesting that the addition of Mg does promote the wettability of SiC by molten Al. The role of the Mg addition on the wetting was presumably attributed to its deoxidation as well as the inhibition of the interfacial reaction between Al and SiC.

Abstract: Grain growth behavior of AlMg5 alloy fabricated by using a new Mg mother alloy containing Al₂Ca (referred to as AlMg5-Al₂Ca hereinafter) was investigated during homogenization and subsequent hot compression test. Normal AlMg5 alloy using a commercial Mg mother alloy showed abnormally grown large grains in its microstructure after homogenization at 520 ̊C for 12hrs, while the grain growth in the AlMg5-Al₂Ca alloy was completely suppressed by formation of stable Al₄Ca during solidification on grain boundary. The compressive flow stress of normal AlMg5 alloy at 400 ̊C was significantly increased after homogenization because of lack of grains having proper slip directions to the applied load. But the flow stress of AlMg5-Al₂Ca alloy showing no grain growth during homogenization was slightly decreased implying lower energy needed for subsequent thermo-mechanical processing.

Abstract: 800x600 Intermetallics are compounds of two metals or of metal(s) and semimetal(s). Their structures are usually different from those of the constituents. Some intermetallics are interesting functional materials, others have attracted attention as high-temperature structural materials. We remind the reader of some fundamentals of solid-state diffusion and to the major techniques for tracer diffusion measurements, interdiffusion studies and the growth kinetics of layers in solid diffusion couples. Starting from self-diffusion, which is the most basic diffusion phenomenon in any solid, the paper covers the main features of diffusion in binary intermetallics from the systems Cu-Zn, Ni-Al, Fe-Al, Mg-Al, Ni-Ge, Ni-Ga, Fe-Si, Ti-Al, Ni-Mn, Mo-Si, Co-Nb and Ni-Nb.. We illustrate the influence of phase transitions on diffusion and point out some common features of diffusion in intermetallics. We discuss in detail diffusion in silicides of iron, molybdenum and of silicides of refractory metals. We also consider aluminides of iron, nickel, and titanium and in the aluminium-magnesium system. We consider diffusion in intermetallics of the cobalt-niobium and nickel-niobium system and in in the Nb-Sn and V-Ga systems. We finish with some remarks about grain boundary diffusion in intermetallics. Normal 0 21 false false false UK X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Calibri","sans-serif";}

Abstract: The paper presented the structure (TEM), morphology and chemical composition (EDS) of the -Al-Mg thin films and Al-Mg-Ni multilayer obtained by pulsed laser deposition (PLD). This films were deposited using Nd:YAG laser. The different process parameters were applied. The Al-Mg film was obtained by application of the laser wavelength (=355 nm) and substrate temperature (Ts) 200 oC. Whereas the Al-Mg-Ni multilayer was produced at lower laser wavelength (=266 nm) and at room temperature of the substrate. For preparation of both films the same laser fluence (q=4.7 J/cm2) was used. The Al-Mg possessed nanocrystalline structure with the areas where only columnar Al crystals occurred. EDS of this thin film exhibited that in the nanocrystalline areas the chemical composition corresponded to the target content of Al and Mg. While Al-Mg-Ni multilayer composed of six layers. In this case Al-Mg layers were thinner then Ni layers. In the multilayer structure the fcc Al0.65Mg0.35 and fcc Ni phases was revealed.

Abstract: The disadvantages of the conventional twin-roll caster for aluminum alloy are low casting speeds and limited choices of alloys that are castable by this processing. It is known that strip casting of aluminum alloy 5182 is very difficult because of their wider freezing zones. The vertical-type high-speed twin-roll caster used in the present study was devised to overcome these disadvantages. Features of the high speed twin roll casters are as below. Mild steel rolls were used in order to increase the casting speed and to be made at a lower equipment cost. Roll coating is produced in casting of Al-Mg alloy. Therefore lubricant, that resists heat transfer, was not used in the present study. Heat transfer between melt and the roll was improved by hydrostatic pressure of the melt. Low superheat casting was carried out in order to improve microstructure of the strip. In the present study, effectiveness of a high-speed twin roll caster for recycling aluminum alloy was investigated. The effects of the high-speed twin roll caster on alleviating the deterioration of mechanical properties by impurities were investigated. Properties of the cast strip were investigated by metalography, a tension test, and a deep drawing test.

Abstract: The effects of strain path reversal, using forward and reverse torsion, on the microstructure evolution in the aluminium alloy AA5052 have been studied using high resolution electron backscatter diffraction. Deformation was carried using two equal steps of forward/forward or forward/reverse torsion at a temperature of 300°C and strain rate of 1s-1 to a total equivalent tensile strain of 0.5. Sections of the as-deformed gauge lengths of both test specimens were then annealed at 400°C for 1 hour in a salt bath in order to investigate their subsequent recrystallisation response. In both strain path histories the deformation substructure in the grains analysed consisted of microband arrays within an equiaxed dislocation cell structure. The material subjected to forward/forward deformation did, however, have a slightly greater number of low angle boundaries, i.e. boundaries < 15° misorientation, whilst the forward/reverse material had some grains containing little evidence of substructure. On annealing both materials had significantly reduced levels of low angle boundaries but only the forward/forward material had an increased number of high angle boundaries and a reduced grain size, indicating recrystallisation had only occurred in this material. This would suggest that the deformation microstructure within the forward/forward condition was sufficient to initiate and maintain recrystallisation whilst the microstructure produced by the forward/reverse test contained insufficient nuclei or internal energy to produce a recrystallised material within 1 hour. Further work is now required at different annealing times in order to determine if the major effect of strain path is on retarding nucleation, growth or both.

Abstract: The effects of strain path reversal on the microstructure in AA5052 have been studied using high resolution EBSD. Deformation was carried out using two equal steps of forward/forward (F/F) or forward/reverse (F/R) torsion at a temperature of 300°C and strain rate of 1s-1 to a total strain of 0.5. In both cases the deformation microstructure in the majority of grains analysed consisted of microband arrays clustering at specific angles to the macroscopic deformation axes. For the F/F condition microbands clustered around -20° and +45° to the maximum principle stress direction, whilst for the F/R condition significantly more spread in microband angle was observed. This suggests that the microbands formed in the forward deformation have or are dissolving and any new microbands formed are related to the deformation conditions of the final strain path. This leads to the conclusion that instantaneous deformation mode determines the orientation of new microbands formed whilst a non-linear strain path history influences the range of misorientation angle in the material through the dissociation of previously formed microbands and the formation of new microbands at the new straining condition, leading to a lower level of misorientation angle. Analysis of material subjected to static annealing at 400°C for 1 hour appears to correspond with these observations as the F/F material was completely recrystallised with a fine grain structure whilst the F/R material had no major signs of recrystallisation.

Abstract: The effect of heat treatment conditions such as atmosphere, temperature, annealing time and alloying elements on the hydrogen content in Al-Mg based alloys was investigated. The hydrogen content after annealing depends on the annealing atmospheres and alloying elements. When annealed in a wet atmosphere, the release of the hydrogen in the Al-Mg alloys to outside and the absorption of hydrogen from atmosphere into Al-Mg alloys are presumed to occur at the same time. The oxide layer on the surface is revealed to prevent the hydrogen from being released to outside. The spheroidal MgO particles can be seen on the surface of Al-Mg alloys after annealing at 550°C. The number of the MgO particles increases with increasing impurity elements such as Si and Fe, reducing the shielding effect against hydrogen permeration. Therefore, the condensation of hydrogen near the surface after annealing occurs more easily in an Al-Mg alloy of a high-purity than that of an ordinary purity.

Abstract: An experimental AA5182 sheet was cold rolled 80%, and tensile specimens removed with orientations 0, 45 and 90 degrees to the rolling direction. Room temperature monotonic tensile tests were performed on the specimens in different recovered states obtained by isothermal annealing at 230°C from 0.1 to 10h. The tests were instrumented to measure instantaneous plastic strain ratio, and unloaded just after incipient necking, but before failure if possible. With annealing the flow curves are characterized by lower strains to the onset of jerky flow, the reappearance of yield point elongation, decrease in work hardening, and increasing ductility. The recovery in substructure was described using a constitutive parameter proportional to the mean slip distance.